Electrolytic capacitor

ABSTRACT

An electrolytic capacitor includes an anode body having a dielectric layer; a solid electrolyte layer in contact with the dielectric layer of the anode body; and an electrolyte solution. The solid electrolyte layer includes a π-conjugated conductive polymer. The electrolyte solution contains a solvent and a solute, and the solvent contains a glycol compound and a sulfone compound. A proportion of the glycol compound contained in the solvent is 10% by mass or more. A proportion of the sulfone compound contained in the solvent is 30% by mass or more. A total proportion of the glycol compound and the sulfone compound contained in the solvent is 70% by mass or more.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/724,303, filed on Oct. 4, 2017, which claims the benefit of JapaneseApplication No. 2016-213668, filed on Oct. 31, 2016, the entiredisclosures of which Applications are incorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to an electrolytic capacitor including asolid electrolyte layer and an electrolyte solution.

2. Description of the Related Art

As small-sized, large capacitance, and low ESR (Equivalent SeriesResistance) capacitors, promising candidates are electrolytic capacitorsincluding an anode body on which a dielectric layer is formed, a solidelectrolyte layer formed so as to cover at least a part of thedielectric layer, and an electrolyte solution. The solid electrolytelayer includes a π-conjugated conductive polymer.

From the viewpoint of reducing the ESR of the electrolytic capacitor,PCT International Publication No. 2014/021333 proposes that theelectrolyte solution contain as a solvent ethylene glycol andγ-butyrolactone. For example, PCT International Publication No.2014/021333 proposes an electrolyte solution containing a solvent thatincludes ethylene glycol, γ-butyrolactone, and sulfolane at ratios of20% by mass, 40% by mass, and 40% by mass, respectively.

SUMMARY

An electrolytic capacitor of the present disclosure includes an anodebody having a dielectric layer; a solid electrolyte layer in contactwith the dielectric layer of the anode body; and an electrolytesolution. The solid electrolyte layer includes a π-conjugated conductivepolymer. The electrolyte solution contains a solvent and a solute. Thesolvent contains a glycol compound and a sulfone compound. A proportionof the glycol compound contained in the solvent is 10% by mass or more.A proportion of the sulfone compound contained in the solvent is 30% bymass or more. A total proportion of the glycol compound and the sulfonecompound contained in the solvent is 70% by mass or more.

According to the present disclosure, there can be provided anelectrolytic capacitor that has a small leakage current and an excellentheat resistance, and can maintain low ESR.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating an electrolyticcapacitor according to an exemplary embodiment of the presentdisclosure;

FIG. 2 is a schematic view illustrating a configuration of a capacitorelement according to the exemplary embodiment;

FIG. 3 is a graph showing permeability of various solvents to a sealingmember in an environment at 105° C.; and

FIG. 4 is a graph showing permeability of the various solvents to thesealing member in an environment at 125° C.

DETAILED DESCRIPTION OF EMBODIMENT

Prior to describing an exemplary embodiment of the present disclosure,problems in a conventional technique are briefly described. A solvent ofan electrolyte solution permeates a sealing member to evaporate outsidean electrolytic capacitor. This may cause a reduction of the electrolytesolution inside the electrolytic capacitor. The reduction of theelectrolyte solution inside the electrolytic capacitor may cause areduction in a proportion of a solid electrolyte layer covered with theelectrolyte solution, so that oxidation deterioration of the solidelectrolyte layer (π-conjugated conductive polymer) occurs and causes anincrease in the ESR. Particularly, exposure of the electrolyticcapacitor to a high temperature environment is further likely to reducethe electrolyte solution in the electrolytic capacitor, so that theoxidation deterioration of the solid electrolyte layer may be promoted.However, a relationship has not sufficiently been studied yet betweencomposition of the solvent of the electrolyte solution and a degree ofthe solvent of the electrolyte solution evaporating outside theelectrolytic capacitor.

In addition, for reducing the leakage current of the electrolyticcapacitor, it is important for the electrolyte solution to have afunction of restoring a defective part of a dielectric layer (oxidefilm).

In view of circumstances described above, the present disclosureprovides an electrolytic capacitor that has a small leakage current andan excellent heat resistance, and can maintain low ESR.

The electrolytic capacitor according to the present disclosure includesan anode body having a dielectric layer; a solid electrolyte layer incontact with the dielectric layer; and an electrolyte solution. Thesolid electrolyte layer includes a π-conjugated conductive polymer, andthe electrolyte solution contains a solvent and a solute. The solventcontains a glycol compound and a sulfone compound. A proportion of theglycol compound contained in the solvent is 10% by mass or more, aproportion of the sulfone compound contained in the solvent is 30% bymass or more, and a total proportion of the glycol compound and thesulfone compound contained in the solvent is 70% by mass or more.

The electrolyte solution containing the solvent having the compositiondescribed above can suppress the reduction of the electrolyte solutioncaused by the solvent permeating a sealing member to evaporate outsidethe electrolytic capacitor. Further, the oxidation deterioration of thesolid electrolyte layer (π-conjugated conductive polymer) accompanied bythe reduction of the electrolyte solution can be suppressed.Consequently, the ESR of the electrolytic capacitor can maintain low.Even when the electrolytic capacitor is exposed to a high temperatureenvironment over a long period, the electrolyte solution containing thesolvent having the composition described above can suppress theoxidation deterioration of the solid electrolyte layer so that the heatresistance of the electrolytic capacitor can be improved.

The π-conjugated conductive polymer is considered to be swollen by theglycol compound. A swollen π-conjugated conductive polymer is likely tocause rearrangement, so that orientation or crystallinity of theπ-conjugated conductive polymer is considered to be improved. Thesolvent contains 10% by mass or more of the glycol compound to increasethe orientation or the crystallinity of the π-conjugated conductivepolymer included in the solid electrolyte layer. An increase in theorientation and the crystallinity of the π-conjugated conductive polymerimproves conductivity of the solid electrolyte layer and reduces the ESRof the electrolytic capacitor.

The solvent containing 30% by mass or more of the sulfone compound canincrease dissociability of the solute (salt) contained in theelectrolyte solution. A dissociated solute (particularly, an acidcomponent) can contribute to formation of an oxide film in a defectivepart of the dielectric layer so that the function of the electrolytesolution for restoring the dielectric layer can be improved.Consequently, the leakage current of the electrolytic capacitor can bereduced.

Hereinafter, the present disclosure is more specifically described withreference to the exemplary embodiment. The exemplary embodimentdescribed below, however, is not to limit the present disclosure.

FIG. 1 is a schematic sectional view illustrating an electrolyticcapacitor according to the present exemplary embodiment, and FIG. 2 is aschematic view obtained by developing a part of a capacitor element ofthe electrolytic capacitor.

The electrolytic capacitor includes, for example, capacitor element 10,bottomed case 11 that houses capacitor element 10, sealing member 12that seals an opening of bottomed case 11, base plate 13 that coverssealing member 12, lead wires 14A, 14B that are lead out from sealingmember 12 and penetrate base plate 13, lead tabs 15A, 15B that connectthe lead wires to electrodes of capacitor element 10, respectively, andan electrolyte solution (not shown). Bottomed case 11 is, at a part nearan opening end, processed inward by drawing, and is, at the opening end,curled to swage sealing member 12.

Sealing member 12 is formed of an elastic material containing a rubbercomponent. As the rubber component, there can be used a butyl rubber(IIR), a nitrile rubber (NBR), an ethylene propylene rubber, an ethylenepropylene diene rubber (EPDM), a chloroprene rubber (CR), an isoprenerubber (IR), a Hypalon (trademark) rubber, a silicone rubber, and afluorine-containing rubber. Sealing member 12 may contain fillers suchas carbon black and silica.

Capacitor element 10 is formed of a wound body as illustrated in FIG. 2.The wound body is a semi-finished product of capacitor element 10 andrefers to a capacitor element in which a solid electrolyte layer has notyet been formed between cathode body 22 and anode body 21 on a surfaceof which a dielectric layer is provided. The wound body includes anodebody 21 connected to lead tab 15A, cathode body 22 connected to lead tab15B, and separator 23.

Anode body 21 and cathode body 22 are wound with separator 23 interposedbetween the anode body and the cathode body. An outermost periphery ofthe wound body is fixed with fastening tape 24. FIG. 2 shows partiallydeveloped wound body before the outermost periphery of the wound body isfixed.

Anode body 21 includes a metal foil whose surface is roughened so as tohave projections and recesses, and the dielectric layer is formed on themetal foil having the projections and recesses. A conductive polymer isattached to at least a part of a surface of the dielectric layer to formthe solid electrolyte layer. The solid electrolyte layer may cover atleast a part of a surface of cathode body 22 and/or at least a part of asurface of separator 23. Capacitor element 10 in which the solidelectrolyte layer has been formed is housed in bottomed case 11 togetherwith the electrolyte solution (not shown).

The electrolyte solution housed in bottomed case 11 contains a solventand a solute, and the solvent contains a glycol compound and a sulfonecompound. A proportion of the glycol compound contained in the solventis 10% by mass or more, a proportion of the sulfone compound containedin the solvent is 30% by mass or more, and a total proportion of theglycol compound and the sulfone compound contained in the solvent is 70%by mass or more.

Here, FIGS. 3 and 4 show results of studying permeability of the solventto the sealing member. FIG. 3 shows permeability of various solvents inan environment at 105° C. FIG. 4 shows permeability of the varioussolvents in an environment at 125° C. As a rubber component included inthe sealing member, a butyl rubber is used. Studies are conducted forthree solvents, i.e., ethylene glycol (EG), sulfolane (SL), andγ-butyrolactone (GBL).

In the meantime, an evaluation test of the permeability of the solventto the sealing member is performed by a method described below. When theelectrolytic capacitor shown in FIG. 1 is produced, a predeterminedamount of the solvents described above are housed in bottomed case 11 inplace of the electrolyte solution. Then, bottomed case 11 is sealed withsealing member 12 to produce an electrolytic capacitor for evaluation.The electrolytic capacitor for evaluation is left to stand in apredetermined temperature environment and checked a change in weightover a period during which the electrolytic capacitor is left to stand.In checking the change, the reduced weight of the electrolytic capacitorover the period is defined as an amount of the solvent that haspermeated sealing member 12.

EG and SL show low permeability in both the environments at 105° C. and125° C. Particularly, EG shows low permeability even in the hightemperature environment at 125° C. In contrast, GBL is higher inpermeability than EG and SL, and shows much higher permeability in thehigh temperature environment at 125° C. than in the environment at 105°C. A reason for these results is not clear but is considered to relateto influence of, for example, the rubber component included in thesealing member, a SP (solubility parameter) value of the solvent, andvapor pressure of the solvent. In a high temperature environment at 125°C. or more, the permeability of γ-butyrolactone is considered to befurther increased.

From the results described above, in order to reduce the permeability ofthe solvent even in a high temperature environment at 125° C. or more,it is advantageous to use as the solvent a glycol compound such as EGand a sulfone compound such as SL. It is particularly advantageous touse a glycol compound. On the other hand, in order to increase thefunction of the electrolyte solution for restoring the dielectric layer,it is advantageous to use as the solvent a sulfone compound such as SL.In addition, in order to reduce the ESR, it is advantageous to use, asthe solvent, a glycol compound such as EG.

The inventors of the present disclosure have earnestly studied on abasis of the consideration described above and consequently found to beable to obtain the electrolytic capacitor that has a small leakagecurrent, is excellent in heat resistance, and can maintain low ESR byusing the electrolyte solution containing the solvent having thecomposition described above. Further, the use of such an electrolytesolution can sufficiently suppress the reduction of the electrolytesolution (solvent) even in a high temperature environment at 125° C. ormore, so that the leakage current can be reduced and ESR of theelectrolytic capacitor can maintain low. The use of the solvent havingthe composition described above can sufficiently suppress permeation ofthe solvent to sealing member 12 even in a high temperature environmentat 125° C. or more.

From the viewpoint of reducing the ESR and improving the heat resistanceof the electrolytic capacitor, the proportion of the glycol compoundcontained in the solvent ranges preferably from 10% by mass to 70% bymass, inclusive, more preferably from 30% by mass to 60% by mass,inclusive.

From the viewpoint of increasing the function of restoring thedielectric layer, the proportion of the sulfone compound contained inthe solvent ranges preferably from 30% by mass to 90% by mass,inclusive, more preferably from 40% by mass to 70% by mass, inclusive.

From the viewpoint of reducing the ESR and improving the heat resistanceof the electrolytic capacitor, the total proportion of the glycolcompound and the sulfone compound contained in the solvent is preferably80% by mass or more, more preferably 90% by mass or more.

Examples of the glycol compound include an alkylene glycol and apolyalkylene glycol having a weight average molecular weight of lessthan 300. The glycol compound referred to herein does not include apolyalkylene glycol having a weight average molecular weight of 300 ormore. More specific examples of the glycol compound include ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol, hexyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,pentaethylene glycol, and hexaethylene glycol. These glycol compoundsmay be used alone or in combination of two or more glycol compounds.

Especially, the glycol compound is preferably ethylene glycol. Ethyleneglycol is low in viscosity among glycol compounds, so that ethyleneglycol easily dissolves a solute. Further, ethylene glycol is high inheat conductivity and is excellent in heat dissipation when a ripplecurrent has occurred, so that ethylene glycol has a large effect ofimproving the heat resistance.

The sulfone compound is an organic compound having a sulfonyl group(—SO₂—) in a molecule of the organic compound. Examples of the sulfonecompound include a chain sulfone and a cyclic sulfone. Examples of thechain sulfone include dimethyl sulfone, diethyl sulfone, dipropylsulfone, and diphenyl sulfone. Examples of the cyclic sulfone includesulfolane, 3-methyl sulfolane, 3,4-dimethyl sulfolane, and3,4-diphenyl-methyl sulfolane. Especially, from the viewpoint ofdissociability and thermal stability of a solute, the sulfone compoundis preferably sulfolane. Sulfolane is low in viscosity among sulfonecompounds, so that sulfolane easily dissolves a solute.

The solvent may contain another component than the glycol compound andthe sulfone compound at a proportion of 30% by mass or less. Examples ofthe other component include a lactone compound and a carbonate compound.Examples of the lactone compound include γ-butyrolactone (GBL) andγ-valerolactone. Examples of the carbonate compound include dimethylcarbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC),ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylenecarbonate (FEC). These other components may be used alone or incombination of two or more other components. Especially, from theviewpoint of the thermal stability, the other component is preferably alactone compound, more preferably GBL. Although GBL easily evaporates,using the solvent containing GBL at a proportion of 30% by mass or lesscan suppress the oxidation deterioration of the solid electrolyte layerand a mounting defect of the electrolytic capacitor due to distortion ofthe sealing member caused by an increase in internal pressure of theelectrolytic capacitor, in comparison with a case of using the solventcontaining GBL at a proportion of more than 30% by mass. The proportionof GBL contained in the solvent is preferably 10% by mass or less, andmore preferably, the solvent contains no GBL.

Further, the solvent may contain, as the other component, a polyalkyleneglycol having a weight average molecular weight ranging from about 300to about 1000, inclusive. The solvent containing such a polyalkyleneglycol can suppress generation of a short circuit in the electrolyticcapacitor. Examples of the polyalkylene glycol include polyethyleneglycol, polypropylene glycol, and polybutylene glycol. A proportion ofthe polyalkylene glycol having a weight average molecular weight rangingfrom about 300 to about 1000, inclusive, which is contained in thesolvent, preferably ranges from 5% by mass to 30% by mass, inclusive. Inthe present exemplary embodiment, a polyalkylene glycol having a weightaverage molecular weight of more than 1000 is not to be contained in thesolvent of the electrolyte solution because such a polyalkylene glycolis less likely to dissolve a solute. Further, from the viewpoint ofsuppressing an increase in ESR of the electrolytic capacitor in a lowtemperature environment, the polyalkylene glycol preferably has a weightaverage molecular weight of 600 or less.

The solute preferably includes, as an acid component, an organiccarboxylic acid compound. And the solute preferably includes, as a basecomponent, an amine compound, a quaternary amidinium compound, or aquaternary ammonium compound. The solute preferably includes a primaryto tertiary ammonium salt of an organic carboxylic acid, a quaternaryamidinium salt of an organic carboxylic acid, or a quaternary ammoniumsalt of an organic carboxylic acid. The electrolyte solution containingsuch a solute is excellent in the function of restoring a defective partof the dielectric layer (oxide film) of the anode body so that theleakage current can be reduced. Further, the electrolyte solutioncontaining such a solute is excellent in thermal stability and thereduction of the electrolyte solution is suppressed as described above.Thus, the function restoring a defective part of the dielectric layer issufficiently exhibited over a long period even in a high temperatureenvironment so that the leakage current of the electrolytic capacitorcan maintain low. The base components and solutes exemplified above maybe used alone or in combination of two or more base components andsolutes.

A proportion of the solute that is contained in the electrolyte solutionranges preferably from 5% by mass to 40% by mass, inclusive, morepreferably 10% by mass to 35% by mass, inclusive, the solute including,as the acid component, an organic carboxylic acid compound, the soluteincluding, as the base component, an amine compound, a quaternaryamidinium compound, or a quaternary ammonium compound. The electrolytesolution containing the solute in such ranges sufficiently exhibits thefunction of restoring a defective part of the dielectric layer.

Examples of the organic carboxylic acid compound include aromaticcarboxylic acids such as phthalic acid (ortho), isophthalic acid (meta),terephthalic acid (para), maleic acid, benzoic acid, salicylic acid,trimellitic acid, and pyromellitic acid, and aliphatic carboxylic acidssuch as adipic acid. Especially, from the viewpoint of the function ofthe electrolyte solution for restoring the dielectric layer and thethermal stability of the electrolyte solution, phthalic acid ispreferable.

The amine compound preferably includes at least one selected from thegroup consisting of a primary amine compound, a secondary aminecompound, and a tertiary amine compound. Such an amine compound canincrease the heat resistance of the electrolyte solution to increase thethermal stability of the electrolytic capacitor. As the amine compound,it is possible to use an aliphatic amine, an aromatic amine, and aheterocyclic amine. However, an aliphatic amine having a molecularweight ranging from 72 to 102, inclusive, is preferable because such analiphatic amine has a high degree of dissociation.

Examples of the primary to tertiary amine compound include methyl amine,dimethyl amine, monoethyldimethyl amine, trimethyl amine, ethyl amine,diethyl amine, triethyl amine, ethylene diamine, N,N-diisopropylethylamine, tetramethylethylene diamine, hexamethylene diamine, spermidine,spermine, amantadine, aniline, phenethylamine, toluidine, pyrrolidine,piperidine, piperazine, morpholine, imidazole, imidazoline, pyridine,pyridazine, pyrimidine, pyrazine, and 4-dimethylaminopyridine. Theseamine compounds may be used alone or in combination of two or more aminecompounds. Among these amine compounds, particularly preferred aretertiary amines such as triethyl amine and monoethyldimethyl amine.

The quaternary amidinium compound is preferably a quaternized cyclicamidine compound, and more preferably includes at least one selectedfrom the group consisting of a quaternary imidazolinium compound and aquaternary imidazolium compound. The quaternary amidinium compound is anamidinium cation. Such a quaternary amidinium compound can increaseelectrical conductivity of the electrolyte solution and further reducethe ESR.

Examples of the quaternary imidazolium compound include1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium,1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium,1,3-diethylimidazolium, 1,2-diethyl-3-methylimidazolium, and1,3-diethyl-2-methylimidazolium. Especially, from the viewpoint ofelectrochemical stability, preferred are 1-ethyl-3-methylimidazolium and1-ethyl-2,3-dimethylimidazolium.

Examples of the quaternary imidazolinium compound include1,3-dimethylimidazolinium, 1,2,3-trimethylimidazolinium,1-ethyl-3-methylimidazolinium, 1-ethyl-2,3-dimethylimidazolinium,1,3-diethylimidazolinium, 1,2-diethyl-3-methylimidazolinium,1,3-diethyl-2-methylimidazolinium, and 1,2,3,4-tetramethylimidazolinium.Especially, from the viewpoint of electrochemical stability, preferredare 1,2,3,4-tetramethylimidazolinium and1-ethyl-2,3-dimethylimidazolinium. Examples of the quaternary ammoniumcompound include diethyldimethylammonium and monoethyltrimethylammonium.

In order to further suppress deterioration of the solid electrolytelayer, the acid component is preferred to be included more than the basecomponent. The acid component initially decreases pH of the electrolytesolution to suppress dedoping of a dopant from a conductive polymer. Thesolute including the acid component more than the base component cansuppress the dedoping of a dopant from a conductive polymer and thedeterioration of the solid electrolyte layer accompanied by thededoping. In addition, also in terms of the fact that the acid componentcontributes to the function of the electrolyte solution for restoringthe dielectric layer, the solute is preferred to include the acidcomponent more than the base component.

From the viewpoint of suppressing the deterioration of the solidelectrolyte layer and improving the function of the electrolyte solutionfor restoring the dielectric layer, a molar ratio of the acid componentto the base component (acid component/base component) preferably rangesfrom 1.1 to 10.0, inclusive.

The electrolyte solution preferably further contains a boric acid estercompound. Hydrolysis of a boric acid ester can reduce an amount ofmoisture in the electrolytic capacitor. The reduction of the amount ofmoisture in the electrolytic capacitor can suppress an increase ininternal pressure of the electrolytic capacitor that occurs duringreflow and is caused by vaporization of moisture in the electrolyticcapacitor, and suppress a mounting defect of the electrolytic capacitordue to distortion of the sealing member caused by the increase ininternal pressure of the electrolytic capacitor. In the presentexemplary embodiment, the boric acid ester compound is not contained asthe solvent of the electrolyte solution because the boric acid estercompound dissolves almost no solute.

The boric acid ester compound preferably includes at least one of acondensate of boric acid with a polyalkylene glycol and a condensate ofboric acid with a polyalkylene glycol monoalkyl ether. Examples of thepolyalkylene glycol include polyethylene glycols such as diethyleneglycol and triethylene glycol. A molecular weight of the polyethyleneglycol ranges, for example, from about 100 to about 2000, inclusive.Examples of the polyalkylene glycol monoalkyl ether include polyethylenemonoalkyl ethers such as triethylene glycol monomethyl ether andtetraethylene glycol monoethyl ether. A molecular weight of thepolyethylene monoalkyl ether ranges, for example, from about 120 toabout 2000, inclusive. A content of the boric acid ester compound in awhole electrolyte solution (including the boric acid ester compound)ranges preferably from 5% by mass to 40% by mass, inclusive, morepreferably from 10% by mass to 30% by mass, inclusive.

The solid electrolyte layer includes a π-conjugated conductive polymer.The π-conjugated conductive polymer is preferably, for example,polypyrrole, polythiophene, or polyaniline. These π-conjugatedconductive polymers may be used alone or in combination of two or moreπ-conjugated conductive polymers, or the π-conjugated conductive polymermay be a copolymer of two or more monomers.

In the present specification, polypyrrole, polythiophene, polyaniline,and the like mean polymers having, as a basic skeleton, polypyrrole,polythiophene, polyaniline, and the like, respectively. Therefore,polypyrrole, polythiophene, polyaniline, and the like also includederivatives of polypyrrole, polythiophene, polyaniline, and the like,respectively. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT) and the like.

A weight average molecular weight of the π-conjugated conductive polymeris not particularly limited and ranges, for example, from 1000 to100000, inclusive.

From the viewpoint of suppressing the dedoping of a dopant from theπ-conjugated conductive polymer, the solid electrolyte layer desirablyincludes a polymer dopant. Examples of the polymer dopant include ananion of, for example, polyvinylsulfonic acid, polystyrenesulfonic acid,polyallylsulfonic acid, polyacrylsulfonic acid, polymethacrylsulfonicacid, poly (2-acrylamido-2-methylpropanesulfonic acid),polyisoprenesulfonic acid, and polyacrylic acid. These polymer dopantsmay be used alone or in combination of two or more polymer dopants.These polymer dopants may be a homopolymer or a copolymer of two or moremonomers. Especially, polystyrenesulfonic acid (PSS) is preferable.

A weight average molecular weight of the polymer dopant is notparticularly limited and preferably ranges, for example, from 1000 to500000, inclusive, in terms of facilitating formation of a homogeneoussolid electrolyte layer.

The solid electrolyte layer may be formed by a method for applying asolution containing, for example, a monomer, a dopant, and an oxidant tothe dielectric layer to cause chemical polymerization or electrolyticpolymerization on the dielectric layer. The solid electrolyte layer,however, is preferably formed by a method for applying the π-conjugatedconductive polymer to the dielectric layer in terms of the fact thatexcellent withstand voltage characteristics can be expected. That is,the solid electrolyte layer is preferably formed by impregnating thedielectric layer with a polymer dispersion containing a liquid componentand the π-conjugated conductive polymer dispersed in the liquidcomponent (particularly, a polymer dispersion containing theπ-conjugated conductive polymer and the polymer dopant), forming a filmthat covers at least a part of the dielectric layer, and thenvolatilizing the liquid component from the film. The electrolytesolution described above is particularly effective for suppressingdeterioration of the π-conjugated conductive polymer contained in thepolymer dispersion, and is also effective for improving the orientationof the π-conjugated conductive polymer.

A concentration of the π-conjugated conductive polymer contained in thepolymer dispersion preferably ranges from 0.5% by mass to 10% by mass,inclusive. An average particle diameter D50 of the π-conjugatedconductive polymer preferably ranges from 0.01 m to 0.5 m inclusive, forexample. Here, the average particle diameter D50 is a median diameter ina volume particle size distribution obtained by a particle sizedistribution measuring apparatus according to dynamic light scattering.The polymer dispersion having such a concentration is suitable forforming a solid electrolyte layer having an appropriate thickness and iseasily impregnated into the dielectric layer.

<Method for Producing Electrolytic Capacitor>

Hereinafter, steps of one exemplary method for producing theelectrolytic capacitor according to the present exemplary embodiment aredescribed.

(i) Step of Preparing Anode Body 21 Having Dielectric Layer

First, a metal foil as a raw material for anode body 21 is prepared. Atype of the metal is not particularly limited, but it is preferred touse a valve metal such as aluminum, tantalum, or niobium, or an alloyincluding a valve metal, from the viewpoint of facilitating formation ofthe dielectric layer.

Next, a surface of the metal foil is roughened. A plurality ofprojections and recesses are formed on the surface of the metal foil bythe roughening. The roughening is preferably performed by etching themetal foil. The etching may be performed by, for example, adirect-current electrolytic method or an alternating-currentelectrolytic method.

Next, a dielectric layer is formed on the roughened surface of the metalfoil. A method for forming the dielectric layer is not particularlylimited, and the dielectric layer can be formed by subjecting the metalfoil to an anodizing treatment. The anodizing treatment is performed by,for example, immersing the metal foil in an anodizing solution such asan ammonium adipate solution followed by a heat treatment. The anodizingtreatment may also be performed by applying a voltage to the metal foilthat has been immersed in the anodizing solution.

Normally, a large foil of, for example, a valve metal (metal foil) issubjected to the roughening treatment and the anodizing treatment fromthe viewpoint of mass productivity. In this case, the treated foil iscut into a desired size to prepare anode body 21.

(ii) Step of Preparing Cathode Body 22

A metal foil can also be used for cathode body 22 as with the anodebody. A type of the metal is not particularly limited, but it ispreferred to use a valve metal such as aluminum, tantalum, or niobium,or an alloy including a valve metal. A surface of cathode body 22 may beroughened as necessary.

(iii) Producing of Wound Body (Capacitor Element 10)

Next, anode body 21 and cathode body 22 are used to produce a woundbody. First, anode body 21 and cathode body 22 are wound with separator23 interposed between the anode body and the cathode body. At this time,the winding can be conducted while lead tabs 15A, 15B are rolled in theanode body, the cathode body, and the separator, to cause lead tabs 15A,15B to stand up from the wound body as illustrated in FIG. 2.

As a material for separator 23, a nonwoven fabric can be used thatincludes, as a main component, for example, natural cellulose, syntheticcellulose, polyethylene terephthalate, vinylon, or an aramid fiber.

A material for lead tabs 15A, 15B is not also particularly limited aslong as the material is a conductive material. A material for lead wires14A, 14B connected to lead tabs 15A, 15B, respectively, is not alsoparticularly limited as long as the material is a conductive material.

Next, fastening tape 24 is disposed on an outer surface of cathode body22 positioned at an outermost layer of wound anode body 21, cathode body22, and separator 23, to fix an end of cathode body 22 with fasteningtape 24. When anode body 21 is prepared by cutting a large metal foil,the wound body may further be subjected to an anodizing treatment inorder to provide a dielectric layer on a cut surface of anode body 21.

(iv) Step of Forming Capacitor Element 10

Next, the dielectric layer is impregnated with a polymer dispersion toform a film covering at least a part of the dielectric layer. Thepolymer dispersion contains a liquid component and a π-conjugatedconductive polymer dispersed in the liquid component. The polymerdispersion may be a solution obtained by dissolving the π-conjugatedconductive polymer in the liquid component, or a dispersion liquidobtained by dispersing particles of the π-conjugated conductive polymerin the liquid component. Next, the formed film is dried to volatilizethe liquid component from the film, forming a dense solid electrolytelayer covering at least a part of the dielectric layer. The polymerdispersion is uniformly distributed in the liquid component to easilyform a uniform solid electrolyte layer. Thus, capacitor element 10 canbe obtained.

The polymer dispersion can be obtained by, for example, a method fordispersing the π-conjugated conductive polymer in the liquid componentor a method for polymerizing a precursor monomer in the liquid componentand generating particles of the π-conjugated conductive polymer.Preferable examples of the polymer dispersion include poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid(PSS), i.e., PEDOT/PSS. Although an antioxidant for the π-conjugatedconductive polymer may be added, it is unnecessary to use an antioxidantbecause PEDOT/PSS is unlikely to oxidize.

The liquid component may be water, a mixture of water and a nonaqueoussolvent, or a nonaqueous solvent. The nonaqueous solvent is notparticularly limited, and a protic solvent and an aprotic solvent can beused, for example. Examples of the protic solvent include alcohols suchas methanol, ethanol, propanol, butanol, ethylene glycol, and propyleneglycol, formaldehyde, and ethers such as 1,4-dioxane. Examples of theaprotic solvent include amides such as N-methylacetamide,N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methylacetate, and ketones such as methyl ethyl ketone.

The method for applying the polymer dispersion to a surface of thedielectric layer is preferably a method for immersing the wound body inthe polymer dispersion housed in a container because the method issimple. An immersion period depends on a size of the wound body, butranges, for example, from 1 second to 5 hours, inclusive, preferablyfrom 1 minute to 30 minutes, inclusive. In addition, impregnation ispreferably performed under a reduced pressure, in an atmosphere ranging,for example, from 10 kPa to 100 kPa, inclusive, preferably from 40 kPato 100 kPa, inclusive. Further, ultrasonic vibration may be applied tothe wound body or the polymer dispersion while the wound body isimmersed in the polymer dispersion. The drying after picking the woundbody up from the polymer dispersion is performed at a temperatureranging preferably from 50° C. to 300° C., inclusive, more preferablyfrom 100° C. to 200° C., inclusive, for example.

The step of applying the polymer dispersion to the surface of thedielectric layer and the step of drying the wound body may be repeatedtwo or more times. These steps can be performed a plurality of times toincrease coverage of the solid electrolyte layer on the dielectriclayer. In the steps, the solid electrolyte layer may be formed on notonly the surface of the dielectric layer but also surfaces of cathodebody 22 and separator 23.

As described above, the solid electrolyte layer is formed between anodebody 21 and cathode body 22 to produce capacitor element 10. The solidelectrolyte layer formed on the surface of the dielectric layer actuallyfunctions as a cathode material.

(v) Step of Preparing Electrolyte Solution and Impregnating CapacitorElement 10 with Electrolyte Solution

Next, a solute (an acid component and a base component) is dissolved ina solvent to prepare an electrolyte solution, and then capacitor element10 is impregnated with the electrolyte solution. A method forimpregnating capacitor element 10 with the electrolyte solution is notparticularly limited. For example, a method for immersing capacitorelement 10 in the electrolyte solution housed in a container is simpleand preferred. An immersion period depends on a size of capacitorelement 10, and ranges, for example, from 1 second to 5 minutes,inclusive. Impregnation is preferably performed under a reducedpressure, in an atmosphere ranging, for example, from 10 kPa to 100 kPa,inclusive, preferably from 40 kPa to 100 kPa, inclusive.

(iv) Step of Encapsulating Capacitor Element

Next, capacitor element 10 is encapsulated. Specifically, first,capacitor element 10 is housed in bottomed case 11 so that lead wires14A, 14B are positioned on an open upper surface of bottomed case 11. Asa material for bottomed case 11, there can be used metals such asaluminum, stainless steel, copper, iron and brass, or alloys of thesemetals.

Next, sealing member 12 formed so as to allow lead wires 14A, 14B topenetrate the sealing member is disposed above capacitor element 10 toencapsulate capacitor element 10 in bottomed case 11. Next, bottomedcase 11 is, at a part near an opening end, processed by transversedrawing, and is, at the opening end, curled to swage sealing member 12.Then, base plate 13 is disposed on a curled part of the bottomed case tocomplete the electrolytic capacitor as illustrated in FIG. 1. Then, anaging treatment may be performed while a rated voltage is applied.

In the exemplary embodiment described above, a wound electrolyticcapacitor has been described. The application range of the presentdisclosure, however, is not limited to the wound electrolytic capacitorand can also be applied to other electrolytic capacitors such as a chipelectrolytic capacitor including a metal sintered body as an anode body,and a laminated electrolytic capacitor including a metal plate as ananode body.

EXAMPLES

Hereinafter, the present disclosure is described in more detail withreference to examples. The present disclosure, however, is not limitedto the examples.

Examples 1 to 16 and Comparative Examples 1 to 6

In the present example, a wound electrolytic capacitor (Φ10.0 mm×L(length) 10.0 mm) having a rated voltage of 25 V and a ratedelectrostatic capacity of 330 μF was produced. Hereinafter, a specificmethod for producing the electrolytic capacitor is described.

(Preparation of Anode Body)

A 105-μm-thick aluminum foil was subjected to etching to roughen asurface of the aluminum foil. Then, a dielectric layer was formed on thesurface of the aluminum foil by an anodizing treatment. The anodizingtreatment was performed by immersing the aluminum foil in an ammoniumadipate solution and applying a voltage of 45 V to the aluminum foil.Then, the aluminum foil was cut into a size of 5.3 mm (length)×180 mm(width) to prepare an anode body.

(Preparation of Cathode Body)

A 50-μm-thick aluminum foil was subjected to etching to roughen asurface of the aluminum foil. Then, the aluminum foil was cut into asize of 5.3 mm (length)×180 mm (width) to prepare a cathode body.

(Producing of Wound Body)

An anode lead tab and a cathode lead tab were connected to the anodebody and the cathode body, respectively, and the anode body and thecathode body were wound with a separator interposed between the anodebody and the cathode body while the lead tabs were rolled in the anodebody, the cathode body, and the separator. Ends of the lead tabsprotruding from the wound body were connected to an anode lead wire anda cathode lead wire, respectively. Then, the produced wound body wassubjected to an anodizing treatment again to form a dielectric layer ata cutting end of the anode body. Next, an end of an outer surface of thewound body was fixed with a fastening tape to complete the wound body.

(Preparation of Polymer Dispersion)

A mixed solution was prepared by dissolving 3,4-ethylenedioxythiopheneand a polymer dopant, i.e., polystyrenesulfonic acid (PSS, weightaverage molecular weight 100000) in ion-exchanged water (liquidcomponent). While the mixed solution was stirred, iron (III) sulfate(oxidant) that had been dissolved in ion-exchanged water was added tothe mixed solution to cause a polymerization reaction. After thereaction, a resultant reaction solution was dialyzed to remove unreactedmonomers and an excessive oxidant, so that a polymer dispersion wasobtained that contained about 5% by mass of poly (3,4-ethylenedioxythiophene) doped with PSS (PEDOT/PSS).

(Formation of Solid Electrolyte Layer)

The wound body was immersed in the polymer dispersion housed in apredetermined container in a reduced-pressure atmosphere (40 kPa) for 5minutes, and then the wound body was picked up from the polymerdispersion. Next, the wound body that had been impregnated with thepolymer dispersion was dried in a drying furnace at 150° C. for 20minutes to form a solid electrolyte layer covering at least a part ofthe dielectric layer.

(Preparation of Electrolyte Solution)

Ethylene glycol (EG) as a glycol compound, sulfolane (SL) as a sulfonecompound, and γ-butyrolactone (GBL) as a lactone compound were used as asolvent of an electrolyte solution. For an acid component of a solute,phthalic acid (ortho) was used as an organic carboxylic acid compound.For a base component of the solute, triethyl amine (tertiary aminecompound) was used as an amine compound. The solvent and the solute wereused to prepare an electrolyte solution.

A ratio among EG, SL, and GBL contained in the solvent was set to thevalues shown in Tables 1 to 3. A content of the solute in a wholeelectrolyte solution was set to 25% by mass. A molar ratio of the acidcomponent to the base component (acid component/base component) was setto 2.5. At least a part of the acid component (phthalic acid) was addedas a salt (triethylamine phthalate) with the base component (triethylamine).

(Impregnation with Electrolyte Solution)

The capacitor element was immersed in the electrolyte solution for 5minutes in a reduced-pressure atmosphere (40 kPa) to impregnate thecapacitor element with the electrolyte solution.

(Encapsulation of Capacitor Element)

The capacitor element that had been impregnated with the electrolytesolution was encapsulated to complete an electrolytic capacitor.Specifically, the capacitor element was housed in a bottomed case sothat lead wires were positioned on an opening side of the bottomed case,and a sealing member (an elastic material including a butyl rubber as arubber component) that was formed so as to allow the lead wires topenetrate the sealing member was disposed above the capacitor element sothat the capacitor element was encapsulated in the bottomed case. Thebottomed case was, at a part near an opening end, processed by drawingand was further curled at the opening end. And a base plate was disposedon a curled part to complete the electrolytic capacitor as illustratedin FIG. 1. Then, an aging treatment was performed at 100° C. for 2 hourswhile a voltage of 39 V was applied.

(Evaluation)

(a) Measurement of ESR

An ESR value (initial ESR value: X0) (mΩ) at a frequency of 100 kHz wasmeasured in an environment at 20° C. for the electrolytic capacitor withan LCR meter for 4-terminal measurement. Further, in order to evaluatelong term stability, the rated voltage was applied to the electrolyticcapacitor at a temperature of 145° C. for 500 hours, and then the ESRvalue (X1) (mΩ) was measured by the same method as described above.Then, an increasing rate of the ESR (ΔESR) was acquired by an equationbelow.ΔESR (%)=(X1−X0)/X0×100(b) Measurement of Occurrence Rate of Swelling in Electrolytic Capacitor

Ten electrolytic capacitors were prepared for each of the examples andcomparative examples. Then, each of the electrolytic capacitors wasmeasured with a microgauge for lengths α1 and β1 in FIG. 1. Then, theelectrolytic capacitor was left to stand for 5 minutes while heated at200° C., and the heated electrolytic capacitor was measured for lengthsα2 and β2 in FIG. 1. Subsequently, a swelling amount of the sealingmember was acquired by an equation below.Swelling amount (mm)=(β2−β1)−(α2−α1)

An average value of 10 swelling amounts was acquired.

(c) Measurement of Leakage Current

The rated voltage was applied to the electrolytic capacitor in anenvironment at 20° C., and a leakage current (initial) was measured 2minutes after the application. Further, in order to evaluate long termstability, the rated voltage was applied to the electrolytic capacitorat a temperature of 145° C. for 500 hours, and then the leakage current(after the electrolytic capacitor was left to stand at the hightemperature) was measured by the same method as described above. Tables1 to 3 show evaluation results.

TABLE 1 Evaluation Composition of Leakage electrolyte solution currentContent of components Average Leakage (after left to in solvent Initialswelling current stand at high EG + ESR ΔESR amount (initial)temperature) EG SL SL GBL (Ω) (%) (mm) (μA) (μA) Comparative — — — 1000.25 178 0.36 3.19 3.46 Example 1 Comparative 100 — — — 0.10 15 0.073.21 35.51 Example 2 Comparative — 100 — — 0.25 108 0.08 3.23 3.65Example 3 Comparative 20 40 60 40 0.015 75 0.18 3.15 3.36 Example 4Example 1 25 45 70 30 0.013 40 0.10 3.08 3.18 Example 2 30 50 80 200.012 34 0.09 3.30 3.25 Example 3 35 55 90 10 0.012 22 0.07 3.11 3.26Example 4 40 60 100 — 0.010 20 0.08 3.21 3.18 EG: ethylene glycol, SL:sulfolane, GBL: γ-butyrolactone

TABLE 2 Evaluation Composition of Leakage electrolyte solution currentContent of components Average Leakage (after left to in solvent Initialswelling current stand at high EG + ESR ΔESR amount (initial)temperature) EG SL SL GBL (Ω) (%) (mm) (μA) (μA) Comparative 5 65 70 300.025 112 0.13 3.36 3.33 Example 5  Example 5  10 60 70 30 0.018 73 0.123.28 3.25 Example 6  15 55 70 30 0.015 72 0.11 3.12 3.18 Example 7  2050 70 30 0.014 70 0.10 3.33 3.12 Example 1  25 45 70 30 0.013 40 0.103.08 3.18 Example 8  30 40 70 30 0.013 31 0.10 2.98 3.21 Example 9  3535 70 30 0.012 24 0.09 3.06 3.18 Example 10 40 30 70 30 0.010 22 0.093.12 3.17 Comparative 45 25 70 30 0.012 23 0.08 3.20 5.18 Example 6  EG:ethylene glycol, SL: sulfolane, GBL: γ-butyrolactone

TABLE 3 Evaluation Composition of Leakage electrolyte solution currentContent of components Average Leakage (after left to in solvent Initialswelling current stand at high EG + ESR ΔESR amount (initial)temperature) EG SL SL GBL (Ω) (%) (mm) (μA) (μA) Example 11 10 90 100 —0.19 27 0.08 3.12 3.23 Example 12 20 80 100 — 0.15 24 0.08 3.21 3.24Example 13 30 70 100 — 0.13 22 0.08 3.36 3.11 Example 4  40 60 100 —0.010 20 0.08 3.21 3.18 Example 14 50 50 100 — 0.010 19 0.07 3.22 3.25Example 15 60 40 100 — 0.010 18 0.07 3.32 3.36 Example 16 70 30 100 —0.010 17 0.07 3.29 4.01 EG: ethylene glycol, SL: sulfolane, GBL:γ-butyrolactone

In Examples 1 to 16, low ESR and a low leakage current were maintainedover a long period, and excellent heat resistance was obtained. Inaddition, the average swelling amount was small in Examples 1 to 16.

In Comparative Example 1 where only GBL that easily evaporated was usedas the solvent, the average swelling amount increased. In ComparativeExample 1, the electrolytic capacitor was exposed to the hightemperature to increase a reduced amount of the solvent, causing theoxidation deterioration of the solid electrolyte layer to increase theΔESR. In Comparative Examples 1 and 3 where EG was not used for thesolvent, the initial ESR and the ΔESR increased. In Comparative Example2 where SL was not used for the solvent, the function of restoring adefective part of the dielectric layer was deteriorated, increasing theleakage current after the electrolytic capacitor was left to stand atthe high temperature.

In Comparative Example 4 where GBL that easily evaporated was much usedfor the solvent, the electrolytic capacitor was exposed to the hightemperature to increase a reduced amount of the solvent, causing theoxidation deterioration of the solid electrolyte layer to increase theΔESR. In Comparative Example 5, an amount of EG was small to increasethe ΔESR. In Comparative Example 6, because an amount of SL was small,the function of restoring a defective part of the dielectric layer wasdeteriorated, increasing the leakage current after the electrolyticcapacitor was left to stand at the high temperature.

Examples 17 to 22

An electrolytic capacitor was produced in the same manner as in Example1 except that the components of the solvent were changed as shown inTable 4, and the evaluation was performed in the same manner. PG, DEG,and DMS in Table 4 denote propylene glycol, diethylene glycol, anddimethyl sulfone, respectively. PEG300, PEG400, and PEG600 in Table 4denote polyethylene glycols having a weight average molecular weight of300, 400, and 600, respectively. Table 4 shows evaluation results.

TABLE 4 Evaluation Leakage current Composition of Average Leakage (afterleft to electrolyte solution Initial swelling current stand at highGlycol Sulfone Other ESR ΔESR amount (initial) temperature) compoundcompound component (Ω) (%) (mm) (μA) (μA) Example 1  EG SL GBL 0.013 400.10 3.08 3.18 Example 17 PG SL GBL 0.017 52 0.11 3.25 3.16 Example 18DEG SL GBL 0.015 43 0.09 3.33 3.22 Example 19 EG DMS GBL 0.011 38 0.082.99 3.15 Example 20 EG SL PEG300 0.011 25 0.07 3.18 3.20 Example 21 EGSL PEG400 0.013 28 0.07 3.21 3.33 Example 22 EG SL PEG600 0.016 29 0.073.25 3.35EG: ethylene glycol, SL: sulfolane, GBL: γ-butyrolactone, PG: propyleneglycol, DEG: diethylene glycol, DMS: dimethyl sulfone, PEG300:polyethylene glycol having a weight average molecular weight of 300,PEG400: polyethylene glycol having a weight average molecular weight of400, PEG600: polyethylene glycol having a weight average molecularweight of 600

In any of the examples, low ESR and a low leakage current weremaintained over a long period, and excellent heat resistance wasobtained. In any of the examples, the swelling amount was small.

Examples 23 to 27

An electrolytic capacitor was produced in the same manner as in Example1 except that the base component of the solute was changed as shown inTable 5, and the evaluation was performed in the same manner. As aprimary amine compound, ethyl amine was used. As a secondary aminecompound, diethyl amine was used. As a quaternary imidazolium compound,1-ethyl-3-methylimidazolium was used. As a quaternary imidazoliniumcompound, 1,2,3,4-tetramethylimidazolinium was used. As a quaternaryammonium compound, diethyldimethylammonium was used. Table 5 showsevaluation results.

TABLE 5 Evaluation Composition Leakage of current electrolyte (afterleft solution Average Leakage to stand at Base Initial swelling currenthigh component ESR ΔESR amount (initial) temperature) of solute (Ω) (%)(mm) (μA) (μA) Example Primary 0.014 45 0.11 3.16 3.23 23 amine compoundExample Secondary 0.013 43 0.11 3.32 3.31 24 amine compound ExampleTertiary 0.013 40 0.10 3.08 3.18  1 amine compound Example Quaternary0.014 68 0.09 3.25 3.08 25 imidazolium compound Example Quaternary 0.01466 0.09 3.40 3.11 26 imidazolinium compound Example Quaternary 0.014 700.09 3.22 3.37 27 ammonium compound

In any of the examples, low ESR and a low leakage current weremaintained over a long period, and excellent heat resistance wasobtained. In any of the examples, the swelling amount was small.

Examples 28 to 33

An electrolytic capacitor was produced in the same manner as in Example1 except that the boric acid ester compound shown in Table 6 was furtheradded to the electrolyte solution, and the evaluation was performed inthe same manner. A content of the boric acid ester compound in the wholeelectrolyte solution was set to 10% by mass, 20% by mass, or 30% bymass. Table 6 shows evaluation results.

TABLE 6 Evaluation Additive added to Leakage electrolyte solutioncurrent Content in Average Leakage (after left to electrolyte Initialswelling current stand at high Boric acid ester solution ESR ΔESR amount(initial) temperature) compound (% by mass) (Ω) (%) (mm) (μA) (μA)Example 1  No additive 0 0.013 40 0.10 3.08 3.18 Example 28 Condensateof 10 0.014 42 0.05 3.26 3.41 Example 29 boric acid with 20 0.013 390.03 3.33 3.16 Example 30 triethylene glycol 30 0.013 37 0.03 3.33 3.25Example 31 Condensate of 10 0.012 39 0.06 3.15 3.21 Example 32 boricacid with 20 0.013 40 0.04 3.42 3.36 Example 33 triethylene glycol 300.012 41 0.04 3.25 3.22 monoethyl ether

In Examples 28 to 33 where the boric acid ester compound was added tothe electrolyte solution, the average swelling amount further decreased.

The present disclosure can be utilized for an electrolytic capacitorthat includes a solid electrolyte layer covering at least a part of adielectric layer, and an electrolyte solution.

What is claimed is:
 1. An electrolytic capacitor comprising: a capacitorelement including an anode body having a dielectric layer and a solidelectrolyte layer in contact with the dielectric layer of the anodebody; a case that houses the capacitor element; an electrolyte solutionthat is contained in the case; and a sealing member that seals anopening of the case, wherein: the solid electrolyte layer includes aπ-conjugated conductive polymer, the electrolyte solution contains asolvent and a solute, the solvent contains a glycol compound other thana polyalkylene glycol having a weight average molecular weight of 300 ormore, a sulfone compound, and a lactone compound, a proportion of theglycol compound contained in the solvent is 10% by mass or more, aproportion of the sulfone compound contained in the solvent is greaterthan 30% by mass, a total proportion of the glycol compound and thesulfone compound contained in the solvent is 70% by mass or more, aproportion of the lactone compound contained in the solvent is more than0% by mass and less than or equal to 30% by mass, and the sealing memberincludes a butyl rubber.
 2. The electrolytic capacitor according toclaim 1, wherein: the solvent further contains the polyalkylene glycolhaving a weight average molecular weight of 300 or more.
 3. Theelectrolytic capacitor according to claim 2, wherein a proportion of thepolyalkylene glycol contained in the solvent ranges from 5% by mass to30% by mass, inclusive.
 4. The electrolytic capacitor according to claim1, wherein the proportion of the sulfone compound contained in thesolvent is more than the proportion of the glycol compound contained inthe solvent.
 5. The electrolytic capacitor according to claim 1, whereinthe proportion of the sulfone compound contained in the solvent isgreater than 40% by mass.
 6. The electrolytic capacitor according toclaim 1, wherein the proportion of the sulfone compound contained in thesolvent is 50% by mass or more and 90% by mass or less.
 7. Theelectrolytic capacitor according to claim 1, wherein the sulfonecompound includes sulfolane.
 8. The electrolytic capacitor according toclaim 1, wherein the lactone compound includes γ-butyrolactone.
 9. Theelectrolytic capacitor according to claim 1, wherein the proportion ofthe glycol compound contained in the solvent ranges from 10% by mass to70% by mass, inclusive.
 10. The electrolytic capacitor according toclaim 1, wherein the glycol compound includes at least one selected fromthe group consisting of ethylene glycol, propylene glycol, butyleneglycol, pentylene glycol, hexylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, pentaethylene glycol, andhexaethylene glycol.
 11. The electrolytic capacitor according to claim1, wherein the glycol compound includes ethylene glycol.
 12. Theelectrolytic capacitor according to claim 1, wherein: the soluteincludes an acid component and a base component, and a proportion of thesolute contained in the electrolyte solution ranges from 10% by mass to40% by mass, inclusive.
 13. The electrolytic capacitor according toclaim 12, wherein: the acid component includes an organic carboxylicacid compound, and the base component includes at least one selectedfrom the group consisting of an amine compound, a quaternary amidiniumcompound, and a quaternary ammonium compound.
 14. The electrolyticcapacitor according to of claim 13, wherein the amine compound includesat least one selected from the group consisting of a primary aminecompound, a secondary amine compound, and a tertiary amine compound. 15.The electrolytic capacitor according to of claim 13, wherein thequaternary amidinium compound includes at least one selected from thegroup consisting of a quaternary imidazolinium compound and a quaternaryimidazolium compound.
 16. The electrolytic capacitor according to ofclaim 1, wherein the electrolyte solution further contains a boric acidester compound.
 17. The electrolytic capacitor according to of claim 1,wherein the proportion of the lactone compound contained in the solventis 10% by mass or more.